It is known that processing, disposal and/or destruction of highly toxic waste and substances are done using the following methods:                thermal: burning in air media; plasma-chemical;        chemical: neutralization and chemical reduction;        biological; using special species of anaerobic and aerobic microorganisms (U.S. Pat. No. 5,196,949A).        
The abovementioned methods and technologies for processing and destroying highly toxic substances are complicated, expensive, unsafe and not universal.
Researchers and developers are constantly seeking new engineering and technological solutions for deactivation of toxic substances and waste. Processes of hydrothermal oxidation of organic and inorganic substances in nearly critical and supercritical fluids have been actively studied in the past few years. With the temperature exceeding 374.2° C. and the pressure exceeding 21.8 MPa water transforms into a supercritical substance which is called a fluid. Under those conditions water receives special properties which differ from those of its liquid and gaseous phases. Water turns from a polar fluid into a non-polar fluid and can dissolve hydrophobic chemical compounds. However, at the same time water cannot dissolve many inorganic alkalis. Supercritical water has unlimited thermodynamic compatibility with organic compounds and oxygen, the diffusion speed increases while the oxidizing ability sharply increases. The speed of organic substance oxidation reactions in supercritical fluids is comparable with the speed of similar reactions during the burning of fuels in air media with the combustion front temperature of 2.300 to 2.800 K.
We know the methods of conducting oxidation processes for various classes of organic compounds in supercritical fluid and reactors in which these reactions take place [P. E. Savage, S. Gopalan. T. I. Mizan, Ch. J. Martino, E. E. Brock. Reactions at supercritical conditions: Applications and fundamentals. AlChE Journal, 1995, 41, 1723-1778; U.S. Pat. No. 5,723,045, Mar. 3, 1998].
The main way of industrial production of aluminum hydroxides is the Bayer process and their subsequent drying and calcination brings to production of aluminum oxide. However, conventional methods for producing aluminum hydroxide do not provide achievement of high purity (and structure homogeneity) of the product.
A method of producing aluminum in the form of boehmite (γ AlO(OH)) is known (U.S. Pat. No. 2,758,011, cl. 423-627, Universal Oil Products Co, pub. Aug. 7, 1956 20] which comprises the reaction being carried out in an autoclave where the water and aluminum in the form of fine particles are loaded. Then mixture is heated to a temperature of 482-705° F. (250-374° C.) after which stirring is started at the same temperature under a pressure sufficient to maintain water in the liquid phase. The process is conducted for a time sufficient to interaction of aluminum. In the given examples, the time is about 4 hours. Once all the aluminum has reacted, the stirring is stopped, the autoclave with reaction mixture is cooled, and the resulting aluminum hydroxide is separated. Installation for carrying out the process comprises a reactor with a stirrer, a water inlet and powdered aluminum openings, a sump, a condenser for receiving the vapor gas. Such method on a commercial scale is not technological because of its periodic mode, a method does not allow to produce boehmite and hydrogen with the necessary intensity for industrial applications.
A method of producing aluminum hydroxide is known [U.S. Pat. No. 5,225,229, Cl. 423/629, Aluminum Company of America, pub. Jun. 7, 1993] in which aluminum is in the reaction with water in the liquid phase at a pH of about 12.4. At this pH aluminum hydroxide is produced at an acceptable rate for particles with a specific surface area value from 20000 mm2/g to 75000 mm2/g. In accordance with another type of method to this patent, an organic compound—chlorin is added into the water as a catalyst. A disadvantage of the method is the need to raise the pH, which is achieved by adding a substantial amount of substances providing such a high pH. This method does not provide the desired product purity. Furthermore, the process proceeds at an insufficient rate.
A method of producing gaseous hydrogen is known [U.S. Pat. No. 6,638,493, Cl. 423/657, Andersen, et al., pub. 28 Oct. 2003], which comprises reacting aluminum with water in the presence of sodium hydroxide as a catalyst. In accordance with one aspect of the invention, the process comprises the following steps: creating of an aqueous alkaline solution in the reactor containing from 0.26 M to 19 M NaOH (mole concentration, M), the following step is the molar reaction of aluminum with water on the surface of the solution, while the sludge is lowered from the area of fluidized bed to the bottom of reactor, which prevents the mixing of sludge with the aluminum in the reactor. Since the reaction occurs in a fluidized bed on the surface of the solution, the most part of the reactor volume is not used in the reaction, which determines the lack of efficiency of the process of hydrogen. High levels of NaOH in the resulting aluminum hydroxide in this way considerably complicate its implementation as a commercial product that does not allow reducing the cost of the process.
The main setbacks of these methods are low speeds of chemical reactions and low conversion factors.
Inventions proposing oxidation of various substances and wastes in supercritical fluid in flow-through high-pressure reactors [WO 91/11394, Aug. 8, 1991; U.S. Pat. No. 5,558,783, Sep. 24, 1996; U.S. Pat. No. 5,591,415, Jan. 7, 1997; U.S. Pat. No. 6,264,844, Jul. 24, 2001] are the closest options. They use air, oxygen, oxygen-containing gas, hydrogen peroxide, nitric acid and perchlorate as oxidizing agents. Limited time for contact between reacting agents leading to low conversion factors is the disadvantage of these reactors.
In a specific realisation, the invention is aimed to provide a process for the continuous producing of chemically pure, fully crystallized by its structure aluminum hydroxide—boehmite (AlO(OH)), and hydrogen using aluminum powder having a particle size up to 60 microns. Such technical problems as increasing the reliability and stability of work of the reactor are solved.
The essence of the method for producing the nanocrystalline aluminum hydroxide in the form of boehmite and hydrogen, comprising preparing a slurry of powdered aluminum in the water, creating a pressure and temperature of saturated water vapor in the reactor corresponding to the conditions of intensive oxidation of aluminum, spraying the slurry in the reactor, output of mixture of water vapor and hydrogen from the reactor, and the output of boehmite from the reactor to the receiving device is that, when preparing the slurry of powdered aluminum in water, it comprises the catalyst—an alkali metal hydroxide in an amount of not more than 0.1 M (M—molar concentration), and after spraying the slurry prior to output of boehmite from the reactor allowance of the slurry to final oxidation of aluminum and the crystallization of the boehmite is carried out.
Furthermore, a process for producing nanocrystalline aluminum hydroxide in the form of boehmite and hydrogen is proposed, wherein for obtaining the continuity of the process of boehmite and hydrogen at least one auxiliary reactor is used, wherein during spraying the slurry in one of the reactors at least in one of other reactors additional oxidation of aluminum, the crystallization of boehmite are performed and output of boehmite is produced.